The term “granular material” refers to granular to powdery, easily pourable solid matter, for example grit or fine sand, such as is used for the improvement of the braking effect between the wheels of vehicles and the roadway. For instance, in the case of rail-bound vehicles, granular material or sand from a container is conveyed via a metering and conveying device via a nozzle in front of the rail wheels and into the gap between the rail wheel and the rail, to increase the frictional resistance between the rail wheel and the rail and reduce the breaking distance.
For example, the AT 505 783 B1 describes such a spreader, wherein metering of the grit takes place via a rotating star feeder.
Another discharge device, in which metering and conveying of the grit are effected by means of compressed air, is known e. g. from WO 2008/064747 A1.
In particular when using a relatively hard granular material, for example, quartz sand, there exists the problem of the components of the discharge device being subjected to relatively fast wear and tear, since the granular material or the sand leads to an accelerated deterioration of the discharge function or even to a malfunction due to the friction on the components of the discharge device. Using high-quality and durable materials for the components of the discharge device did not result in essential improvements, since blockades may occur in the process, whenever the hard granular material encounters moving parts of the discharge device likewise made of a hard material. Therefore, better results could be obtained when using softer, but also less durable materials, in particular for the moved parts of the discharge device. For example, star feeders are frequently made of plastics, reducing the service life considerably, however. Replacing the parts subject to wear and tear results in downtimes and assembly costs that are undesirable in most cases. In particular, in the case of discharge devices such as are frequently used in rail-bound vehicles, low downtimes and short maintenance intervals are not desired.